In the conventional process for forming rubber stamps or printing plates, a photographic negative bearing printing or indicia is applied to a surface of a photosensitive plastic sheet. The composite structure is exposed to ultraviolet light, and the ultraviolet light causes a chemical reaction to occur in the exposed portions of the photosensitive sheet, thereby hardening the exposed portions. The remaining non-exposed portions of the sheet can be removed by etching using a caustic material, thereby resulting in a type-form sheet having a raised printing or indicia.
In the conventional process, a mold plate is formed by placing a fibrous board with a phenolic resin facing on the type form sheet. Through the application of heat and pressure, the phenolic resin will soften and conform to the raised printing, thereby forming a molding plate having recessed printing.
The molding plate is then used as a mold to form rubber stamps or printing plates of rubber or other materials.
In some cases the printing is extremely small, less than 1/32 inch, and with conventional processes, it is difficult to get full fidelity in the molding plate, with the result that the final printing is not sharply defined.
As a further disadvantage, the phenolic resin coated fiber boards can only be used up to about 5 times for forming a printing plate and then must be discarded due to the fact that the rubber being used to form the printing plate has a tendency to adhere within the grooves of the phenolic coated molding plate.
Furthermore, the phenolic resin coated fiber boards, as commonly used, have a tendency to absorb moisture, and the absorbed moisture tends to cause ink impregnated rubber to be rejected from the mold surface, thereby resulting in defective printing plates.